Thursday, March 29, 2007

Dead Dinos ≠ More Mammals

Abstract:Did the end-Cretaceous mass extinction event, by eliminating non-avian dinosaurs and most of the existing fauna, trigger the evolutionary radiation of present-day mammals? Here we construct, date and analyse a species-level phylogeny of nearly all extant Mammalia to bring a new perspective to this question. Our analyses of how extant lineages accumulated through time show that net per-lineage diversification rates barely changed across the Cretaceous/Tertiary boundary. Instead, these rates spiked significantly with the origins of the currently recognized placental superorders and orders approximately 93 million years ago, before falling and remaining low until accelerating again throughout the Eocene and Oligocene epochs. Our results show that the phylogenetic 'fuses' leading to the explosion of extant placental orders are not only very much longer than suspected previously, but also challenge the hypothesis that the end-Cretaceous mass extinction event had a major, direct influence on the diversification of today's mammals.

A new, complete 'tree of life' tracing the history of mammals on Earth shows that they did not diversify as a result of the death of the dinosaurs. It contradicts the previously accepted theory that the Mass Extinction Event that wiped out the dinosaurs 65 million years ago prompted the rapid rise of the mammals we see on the earth today.

Research shows that after the mass exteinxtion certain mammals did experience a rapid period of diversification and evolution. However, most of these groups have since either died out completely or declined in diversity.

The researchers believe that our 'ancestors', and those of all other mammals on earth now, began to radiate around the time of a sudden increase in the temperature of the planet – ten million years after the death of the dinosaurs.